- One theory regarding evolution proposes that natural selection is less of a factor for people past their reproductive years, as genetic variations are not passed on to offspring at this stage of life.
- A new study supports this idea, finding that certain tissue types in older people are influenced more by aging itself and by environmental factors than by DNA.
- These tissues, while important, can also lead to cancers, suggesting a limit to what evolution can accomplish.
In 1952, Nobel laureate Dr. Peter Medawar hypothesized that aging processes might be the result of evolutionary natural selection having little to say about people. over the childbearing age.
A new study finds new support for the Medawar hypothesis in an analysis of how around 20,000 human genes are
The study suggests that our genes have less influence as we age.
The study’s lead author, Dr. Peter Sudmant, an assistant professor of integrative biology at the University of California, Berkeley, says Berkeley News“Almost all common human diseases are diseases of aging: Alzheimer’s, cancers, heart disease, diabetes.”
“Massive amounts of public resources have been devoted to identifying the genetic variants that predispose you to these diseases. What our study shows is that in fact, as you age, genes have less importance for the expression of your genes,” says Sudmant.
The study is published in
Dr. Sudmant summarized Medawar’s hypothesis for Medical News Today:
“Genes that are activated when we are young are more constrained by evolution because they are essential for ensuring our survival and reproduction, while genes expressed after reaching childbearing age experience less evolutionary pressure.”
Dr Giuseppe Passarino, a professor of genetics at the University of Calabria in Italy, who was not involved in the study, told DTM How does it work :
“Obviously, to have more children, you have to survive and be fit [long enough to] reproduce yourself. To achieve this goal, you need to have no illnesses in your youth, be able to find food, find a partner.
“The genes that are expressed in the first part of your life are highly selected, and then only the best survive.”
— Dr. Giuseppe Passarino
“Evolution is based on the fact that individuals who are in better physical condition have more children. Thus, their genotypes will spread more in the population than those of subjects who have [fewer] children,” added Dr. Passarino.
The researchers retrieved gene expression data for 27 different types of body tissues in nearly 950 people from the GTEx web portal. Individuals were classified as “young” if they were under 55 and “old” if they were 55 or older.
In their analysis, the researchers found that genetics exerts roughly the same influence on gene expression in almost all of our tissues until we pass into the “old” slice.
At this point, aging plays a much more influential role for five critical tissue types – blood, colon, arteries, esophagus, and fatty tissue – than genetics.
As an influence on gene expression in the study, “aging” refers to the universal and progressive processes of cellular aging associated with age.
“In our study, we found in five tissues with high proliferation (blood, colon, etc.), [that] these highly constrained genes are actually activated late in life. These genes tend to be those involved in cell division and proliferation, and therefore, in cancer.
— Dr. Peter Sudmant
While it would theoretically be useful for evolution to help select genes that keep us healthy even after reproduction, according to Dr. Sudmant:
“The ‘evolutionary limit’ here is that, late in life, you really shouldn’t have these kinds of genes turned on, and having them turned on actually makes you vulnerable to cancer. However, because these are types of cells in your body that must continue to renew themselves, blood!—there is no other option.
Therefore, aging and environmental factors are more influential in gene expression for these critical tissues.
In the study, environmental influences include factors that are not directly associated with these processes: the quality of the air and water we breathe and eat, our diet, as well as our level of physical exercise.
The study reveals that environmental factors account for about a third of gene expression in older people.
“This [study] does not imply that genetics is not important for aging. Numerous studies show that the similarities between relatives concerning the quality of aging (presence of diseases or disabilities) are very high. In fact, although the genes expressed later in life are not selected, they are nevertheless important for our life.
— Dr. Giuseppe Passarino
“In other words, we are equipped with highly selected equipment
According to Dr. Passarino, to better understand the complexity of human aging and how to slow down this process, researchers need to study the genes expressed later in life and improve them.
“One option may be to see how the genetic machinery works in long-lived subjects and try to modulate the machinery of others accordingly,” Dr. Passarino said.
“For example, long-lived subjects have been observed to have a limited ability to utilize protein or sugar. Thus, we can use a limited amount of protein and sugar to modulate the machinery of our body as if we were equipped with the same genes of long-lived subjects,” he explained.
“When we perform studies to identify the underlying genetic disease, we often end up with many genes that we could potentially target. Our study now quantifies the impact of age on gene expression in the population. We argue that age-associated genes might be better therapeutic targets than those whose expression varies according to human genetics,” Dr. Sudmant said.
“We believe that genes that show consistency in age-related expression changes in humans are potentially very interesting targets to track!” he concluded.